A constructional large size dump track is formed by mounting a frame on front and further rear wheels and defines a driver's compartment and a vessel for transporting earth, sand or so forth. The frame is subject bending load and a torsional load to possibly cause breakage due to fatigue.
On the other hand, the bending and torsional loads acting on the frame can be significantly differentiated depending upon load weight on the vessel, road surface condition, vehicle speed and so forth. Therefore, it is practically not possible to predict the timing for breakage by fatigue, i.e. a useful life of the frame.
Therefore, in the prior art, a strain gauge is fitted on the frame for measuring a distortion of the strain gauge as an actual strain by means of a measuring equipment during operation for a long period. Based on the measured value, fatigue damage of the frame is calculated through a cumbersome calculation, such as by frequency processing and so forth to predict the useful life.
In such method of for predicting the useful life, of a member it becomes necessary to perform a cumbersome calculation, such as frequency processing and so forth, on the basis of the measured values. Also, only data, representative of an operational condition while the measurement is performed by means of the measuring equipment, can be obtained.